You would have to take them to a muffler shop ... any good shop would be able to use a reducer to go from the stock 2.25" exhaust into the 3" hole on the tips (the outlet size is 4"). Yes, it will have to be welded, and will cost a few bucks at a local shop.
BTW... Happy Birthday, Marine... I was USMC 1987-1994 and US Army 1994-2018.